PHOTORESPONSE OF THE FERROCYANIDE-BROMATE-SULFITE CHEMICAL OSCILLATORUNDER FLOW CONDITIONS

The photoresponse of the ferrocyanide-bromate-sulfite system, known as the pH oscillator, has been studied in the visible region. We have es tablished a state diagram for this system spanned by the flow rate and irradiation light power in a continuous-flow stirred tank reactor. Ph otoinduced oscillations are observed for the system in the low-pH stea dy state in the dark, while the photoinhibition of oscillations are ob served for the system oscillating in the dark. Batch experiments for i ts subsystems (the SO32--BrO3--H+, Fe(CN)(6)(4-)-BrO3--H+ and SO32--Fe (CN)(6)(3-)-H+ systems) have revealed that the positive feedback chann els for H+ (the SO32--BrO3--H+ and SO32--Fe(CN)(6)(3-)-H+ reaction) ar e not sensitive at all to the visible light, while the negative feedba ck channel (the Fe(CN)(6)(4-)-BrO3--H+ reaction) is responsible for th e observed photosensitivity of the whole system. We have confirmed tha t the enhanced formation of Fe(CN)(5)(H2O)(3-) from photoexcited HFe(C N)(6)(3-) is responsible for the photoacceleration of the negative fee dback process.